Jan's post under the dream car spec has got me wondering about tires and pressure. Much of his advice has proven good enough that I'm intrigued at his suggestion of super low tire pressures.
I'd be interested to hear what others have found works best. Charlie? Adam?
After I replaced the rear suspension bushings and did a quick setup, I tried as low as 26psi and as high as 36psi. I didn't think about going lower because I didn't want to lose too much sidewall stability. Given the lack of ability to add static negative camber in the back, I didn't want to sidewall stiffness to go so low as to let the tire start rolling over too far. I ended up at 28psi front and 30psi rear for my first autocross. After every run, I checked and didn't see any scuffing higher up on the sidewalls, but my pressures could have been too high.
Some of the folks at the autocross are real racers with real race cars (SCCA, VSCCA), and all but one of them also drove the Westfield on the course. They all thought the handling was neutral, controllable, and respectable for such an old design. Their best times in the W11 were within 1 hundredth of my time, and to a man they thought the old Sumitomo's were limiting the car's performance (and there was a glaring need for an LSD). We also had some fun practicing our trail braking and spin control on another section of runway. I wouldn't have done this last bit if it weren't for the very wet conditions and the fact that the tires weren't providing enough grip to break anything in the suspension anyway. This last part was big fun and a good chance to start learning a bit about the car's limits.
John
Tire Pressures
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Tire Pressures
When working with very lightweight cars, the loading on the tires is very low, especially when using conventional radial passenger car tires. The W11 is less than half the weight of most cars using those small sized passenger car tires. Remember, the passenger car tires are for cars that are fully loaded to gross weight, including 4 passengers, luggage and full fuel.
With the low weight, low tire pressures are the norm. With the Sumitomos, which I used to run prior to changing to more readily available 185/70s, I ran no more than 20 psi, with the best results at 18 psi. As I drove the car long enough to wear out the old Sumis, I found that in the rear, I was wearing out the middle of the tread at 20 psi, and lowered the pressures to 18 psi, then 17. I had already lowered the front pressures to 17~18 to get even tire wear. Note that my car had a slight front end weight bias of about 1.4% with 170 lbs in the driver's seat and a 3/4 fuel. I run about 1~2 psi more in front than I do in the rear, a result of drive tests, pyrometer data and set up data from the scales.
My guess is that you are using tire pressures about 28% too high, which, in percentages, is, well, too high.
You don't want to set your tire pressures using an arbitrary number, especially if it is printed on the side of a tire that is intended for sedans. Determine your tire pressures by pyrometer, and by feel. If it feels a bit squirmy, and has a quick break away, and locking front brakes, lower the pressures by 2psi at a time until it works right, or use your pyrometer data. I didn't make up my recommended pressures, I arrived at them through testing of three different W11s, using three different tire types, on roads and tracks, using pyrometer data as a base to determine if the tire was giving me all of its tread to work with.
Running the 185/70s, I found that 18 psi seems to work pretty well, and the tire wear has been even so far, at 10K miles. Also, lots more grip with the wider tire.
Forget side wall stability as it is not a factor with tires bearing only 1/3rd of their rated load. The problem is that at 26 psi, the tread loses about 1/3rd of its area. This makes the old Sumis feel greasy, hard and unmanageable. Lower the pressures to 18, and the grip comes back. I can tell you from my own experience with both my 900 lb Lotus 7 and my W11 that 26 is WAY too high. That would be the pressure used on a sedan with a 3000 lb gross weight! No wonder you had to practice spin control, especially with trail braking. You had about an inch of tread working for you in the rear, and I am surprised you had any grip up front. You might take the car for a run, and check the tire temps. You may find 45F or more difference between the center tread, and the outside rib. Oh, and on the lower pressures, it will ride a whole lot better.
On the cars with the bias ply Dunlop vintage race tires, 18~20 psi seems to be the number, with the slightly heavier late chassis working at 20 psi. Watch the rear tires for center tread wear, as sometimes they need pressures as low as 17. On some cars, the center of the front tread may wear a bit too fast at 20 psi. You may want to start at 18 psi, and watch the tread edges for feathering or cupping, and carefully set the camber at about -.5º. Adjust the camber to fix any problems with under steer or wear. These pressures corresponded with the pressures used on my first series Lotus 7 America, which came equipped from the factory with 15" wire wheels, and the racing Dunlops I used for vintage racing. Note that this old 7 chassis was essentially the same as the "Club" version of the Lotus 11, using the same wheels and tires in race trim. I built some adjustable upper arms so that I could set the camber, and optimize the setup.
These pressures are not "ultra low" but normal for cars weighing less than 1400 lbs (on the grid, driver installed) on radial ply or bias ply racing tires. If you don't lower the pressures, you are riding on very thin tires, with only a little of the tread area working for you, making your tires very slippery, indeed. They might even feel as though you need to toss them, as they may be too old. Also, you will get locking of the front brakes during hard braking, as there is no tread working for you to stop the car, even with all the weight transfer.
One of the things that occurs with the lower pressures is that the entire tread can be used, which promotes grip, and makes the transition to over steer a bit softer and easier to control. This transition improves dramatically with the installation of an LSD with a 45/90 engagement ratio. Both braking and cornering are hugely improved. You will notice this at the first corner. Note that the car might feel a little wiggly on the radial side walls. This is normal, and you will get used to it in about 5 miles. It is not instability, but rather the radial tire actually working, keeping the tread on the pavement. After the first few turns, and the discovery of much more G, you will not notice it anymore.
In wet conditions, grip can be slightly improved with a little more pressure, maybe 2PSI on the W11, which would put you at about 20 psi, and expose some of the sharp tread edges to expel water. However, there should be some experimentation, as lower pressures might help as well.
Your experience with the high, sedan weight pressures mirrors my own experience, and I quickly lowered the pressures after the first drive to below 20 PSI. This made for a huge improvement.
Even on my 3400 lb Saleen Mustang Sedan racer, I found in testing that the tire pressures recommended by the tire factory for best lap times were nearly 6 psi too high for maximum grip. This information was taken from my several thousand miles of testing, and tire temp results. Lowering the pressures got me a good two seconds at Willow Springs. Even better was the even tire wear, which allowed an entire season of extra life from my R compound Yokohamas.
My Renault, which weighs only about 2000 lbs, runs tire pressures of only 28 psi in its rear mounted 285/40/15 Yokohamas, rather than the usual 30~36 psi. The difference in tire life is nearly 3X, and the grip nearly .2G, topping out at 1.06G lateral for this mid engine factory rally racer, on 1985 rubber.
Pyrometers are less than $100 US and a great investment, especially if you want to get the most enjoyment and life out of your $1,200 Vintage Dunlops.
With the low weight, low tire pressures are the norm. With the Sumitomos, which I used to run prior to changing to more readily available 185/70s, I ran no more than 20 psi, with the best results at 18 psi. As I drove the car long enough to wear out the old Sumis, I found that in the rear, I was wearing out the middle of the tread at 20 psi, and lowered the pressures to 18 psi, then 17. I had already lowered the front pressures to 17~18 to get even tire wear. Note that my car had a slight front end weight bias of about 1.4% with 170 lbs in the driver's seat and a 3/4 fuel. I run about 1~2 psi more in front than I do in the rear, a result of drive tests, pyrometer data and set up data from the scales.
My guess is that you are using tire pressures about 28% too high, which, in percentages, is, well, too high.
You don't want to set your tire pressures using an arbitrary number, especially if it is printed on the side of a tire that is intended for sedans. Determine your tire pressures by pyrometer, and by feel. If it feels a bit squirmy, and has a quick break away, and locking front brakes, lower the pressures by 2psi at a time until it works right, or use your pyrometer data. I didn't make up my recommended pressures, I arrived at them through testing of three different W11s, using three different tire types, on roads and tracks, using pyrometer data as a base to determine if the tire was giving me all of its tread to work with.
Running the 185/70s, I found that 18 psi seems to work pretty well, and the tire wear has been even so far, at 10K miles. Also, lots more grip with the wider tire.
Forget side wall stability as it is not a factor with tires bearing only 1/3rd of their rated load. The problem is that at 26 psi, the tread loses about 1/3rd of its area. This makes the old Sumis feel greasy, hard and unmanageable. Lower the pressures to 18, and the grip comes back. I can tell you from my own experience with both my 900 lb Lotus 7 and my W11 that 26 is WAY too high. That would be the pressure used on a sedan with a 3000 lb gross weight! No wonder you had to practice spin control, especially with trail braking. You had about an inch of tread working for you in the rear, and I am surprised you had any grip up front. You might take the car for a run, and check the tire temps. You may find 45F or more difference between the center tread, and the outside rib. Oh, and on the lower pressures, it will ride a whole lot better.
On the cars with the bias ply Dunlop vintage race tires, 18~20 psi seems to be the number, with the slightly heavier late chassis working at 20 psi. Watch the rear tires for center tread wear, as sometimes they need pressures as low as 17. On some cars, the center of the front tread may wear a bit too fast at 20 psi. You may want to start at 18 psi, and watch the tread edges for feathering or cupping, and carefully set the camber at about -.5º. Adjust the camber to fix any problems with under steer or wear. These pressures corresponded with the pressures used on my first series Lotus 7 America, which came equipped from the factory with 15" wire wheels, and the racing Dunlops I used for vintage racing. Note that this old 7 chassis was essentially the same as the "Club" version of the Lotus 11, using the same wheels and tires in race trim. I built some adjustable upper arms so that I could set the camber, and optimize the setup.
These pressures are not "ultra low" but normal for cars weighing less than 1400 lbs (on the grid, driver installed) on radial ply or bias ply racing tires. If you don't lower the pressures, you are riding on very thin tires, with only a little of the tread area working for you, making your tires very slippery, indeed. They might even feel as though you need to toss them, as they may be too old. Also, you will get locking of the front brakes during hard braking, as there is no tread working for you to stop the car, even with all the weight transfer.
One of the things that occurs with the lower pressures is that the entire tread can be used, which promotes grip, and makes the transition to over steer a bit softer and easier to control. This transition improves dramatically with the installation of an LSD with a 45/90 engagement ratio. Both braking and cornering are hugely improved. You will notice this at the first corner. Note that the car might feel a little wiggly on the radial side walls. This is normal, and you will get used to it in about 5 miles. It is not instability, but rather the radial tire actually working, keeping the tread on the pavement. After the first few turns, and the discovery of much more G, you will not notice it anymore.
In wet conditions, grip can be slightly improved with a little more pressure, maybe 2PSI on the W11, which would put you at about 20 psi, and expose some of the sharp tread edges to expel water. However, there should be some experimentation, as lower pressures might help as well.
Your experience with the high, sedan weight pressures mirrors my own experience, and I quickly lowered the pressures after the first drive to below 20 PSI. This made for a huge improvement.
Even on my 3400 lb Saleen Mustang Sedan racer, I found in testing that the tire pressures recommended by the tire factory for best lap times were nearly 6 psi too high for maximum grip. This information was taken from my several thousand miles of testing, and tire temp results. Lowering the pressures got me a good two seconds at Willow Springs. Even better was the even tire wear, which allowed an entire season of extra life from my R compound Yokohamas.
My Renault, which weighs only about 2000 lbs, runs tire pressures of only 28 psi in its rear mounted 285/40/15 Yokohamas, rather than the usual 30~36 psi. The difference in tire life is nearly 3X, and the grip nearly .2G, topping out at 1.06G lateral for this mid engine factory rally racer, on 1985 rubber.
Pyrometers are less than $100 US and a great investment, especially if you want to get the most enjoyment and life out of your $1,200 Vintage Dunlops.
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Tire Pressures
Quick note: All tire pressures listed above are set COLD. Hot pressures may be about 4 psi higher, but best to set hot pressures using the pyrometer, making adjustments in 2psi increments.
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xkfeng7
- Posts: 31
- Joined: Mon Aug 13, 2012 3:33 am
- Location: Boston, MA
Re: Tire Pressures
Jan
Sounds good, I'll try theses settings.
John
Sounds good, I'll try theses settings.
John
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Tire Pressures
You might find that those Sumitomos are stickier than you thought. It should also fix your front brake locking and turn in.
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adamwilkinson
- Posts: 187
- Joined: Wed Jun 29, 2011 12:17 pm
Re: Tire Pressures
Just to throw a spanner in the works, I run my tyres at around 26-28 hot (between ~22-24 cold). I found running at 18psi overheated the tyres and caused the to start going 'off'.
I must state that the pressures you run are both tyre dependant and, to a certain extent, driver preference. I run on yoko A048r, 185 (6" rim) front and 205 (8" rim) on rear
Can't comment on pressures for road use though
I must state that the pressures you run are both tyre dependant and, to a certain extent, driver preference. I run on yoko A048r, 185 (6" rim) front and 205 (8" rim) on rear
Can't comment on pressures for road use though
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erictharg
- Posts: 680
- Joined: Thu Jan 29, 2009 7:50 pm
Re: Tire Pressures
Road I have always run between 18 and 20 psi cold. Seems to work fine and give a reasonable ride with both 165/70 x 13 radials and 185/70's. Can't imagine why you'd need to run more than 22 psi. Over 20 the steering gets too light for me. So I'm with Jan on the road settings. If you are worried about sidewall use the old trick of making some chalk marks across the shoulder of the tyre, go out for a sprited drive and see how much chalk you've worn off. I'll wager with 20 psi you won't go beyond the edge of the tread on an Eleven!
For racing, I'm looking for 24 - 25 psi hot which seems to coincide (happily) with around 18 or 19 psi cold.
As Adam says, for racing there is a wide range of what works depnding on tyre sizes, construction, compound and driving style.
For racing, I'm looking for 24 - 25 psi hot which seems to coincide (happily) with around 18 or 19 psi cold.
As Adam says, for racing there is a wide range of what works depnding on tyre sizes, construction, compound and driving style.
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xkfeng7
- Posts: 31
- Joined: Mon Aug 13, 2012 3:33 am
- Location: Boston, MA
Re: Tire Pressures
Many thanks to all
As with many things, the Eleven is not a normal car and I'm sure my experience with other modern/vintage cars will prove invalid.
And yes, I do believe in using pyrometers for tire checking as tire wear as a form of feedback is too slow.
John
As with many things, the Eleven is not a normal car and I'm sure my experience with other modern/vintage cars will prove invalid.
And yes, I do believe in using pyrometers for tire checking as tire wear as a form of feedback is too slow.
John
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xkfeng7
- Posts: 31
- Joined: Mon Aug 13, 2012 3:33 am
- Location: Boston, MA
Re: Tire Pressures
(Tire comments: Jan, the tires I listed are not be DOT legal race tires, but they are still considered solidly in the category of maximum warm weather performers, and not all-season compromises). I would live it if Toyo R888's came in our sizes, but at least we have some better alternatives to junk like these old Sumi's
22lbs: substantial softening of the ride over sharp irregularities. No substantial change in braking grip. Slight dulling of steering feedback/response. Cornering might be a bit better but not a huge improvement (butt-o-meter not accurate enough to be sure when driving on public roads).
18lbs: slight additional softening of the ride over sharp irregularities. No substantial change in braking grip. Quite noticeable softening of steering feedback/response. The slower steering response reduced my ability to manage tail-out driving situations such as trail-braking induced oversteer because larger steering inputs were required and there was a bit more lag between the inputs and the corresponding attitude change.
I'd say 18lbs is too low for my personal preference. I'll try in the vicinity of find a sweet spot..
At all 3 pressures from 18 up to 28 the front tires loose traction easily under heavy braking (no side to side bias). Braking distances are still quite poor compared to my 4000lbs daily beater. And the daily beater has relatively skinny tires for that weight (255/40-17's).
To be fair, I have not tried to optimize the front suspension other than to check toe angle. It doesn't visually have any other obvious problems and the front bearings are fine (a total of 3020 miles on them, no play no noise). The car has very little dive, and weight transfer feels vastly lower than on a typical road car. I suspect this lack of weight is one factor limiting the front braking grip. Possibly, braking could be much improved with better front-rear bias so the fronts don't lock up much earlier than the rears (which is a safe novice-style setup). The rear shoes have not been sent to Porterfield yet and I have no idea what they ar. Also, I've not yet had time to do a dual MC setup with balance bar and there is so much else on the car is not yet optimized.
22lbs: substantial softening of the ride over sharp irregularities. No substantial change in braking grip. Slight dulling of steering feedback/response. Cornering might be a bit better but not a huge improvement (butt-o-meter not accurate enough to be sure when driving on public roads).
18lbs: slight additional softening of the ride over sharp irregularities. No substantial change in braking grip. Quite noticeable softening of steering feedback/response. The slower steering response reduced my ability to manage tail-out driving situations such as trail-braking induced oversteer because larger steering inputs were required and there was a bit more lag between the inputs and the corresponding attitude change.
I'd say 18lbs is too low for my personal preference. I'll try in the vicinity of find a sweet spot..
At all 3 pressures from 18 up to 28 the front tires loose traction easily under heavy braking (no side to side bias). Braking distances are still quite poor compared to my 4000lbs daily beater. And the daily beater has relatively skinny tires for that weight (255/40-17's).
To be fair, I have not tried to optimize the front suspension other than to check toe angle. It doesn't visually have any other obvious problems and the front bearings are fine (a total of 3020 miles on them, no play no noise). The car has very little dive, and weight transfer feels vastly lower than on a typical road car. I suspect this lack of weight is one factor limiting the front braking grip. Possibly, braking could be much improved with better front-rear bias so the fronts don't lock up much earlier than the rears (which is a safe novice-style setup). The rear shoes have not been sent to Porterfield yet and I have no idea what they ar. Also, I've not yet had time to do a dual MC setup with balance bar and there is so much else on the car is not yet optimized.
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Tire Pressures
Set the front end (13" tire) to about 5" ride height (at frame, at about axle centerline), or front lower arms parallel to the ground with the driver installed. Rear can be between 6 and 7" depending on the tire. Steering feedback may be due to improper toe, probably too much toe in, though toe out of 1" can do the same thing. Most of the cars that I have seen have excessive toe out. This is usually due to setting the toe without the driver in the seat.
-1º camber, 1/16" toe in with the driver installed. First click on the dampers (maybe). Steering response should be quick and linear with strong caster return. Front bar (factory type) set with the adjuster about one inch back from the end of the bar.
Front suspension should be free when bounced. Try loosening the bolts slightly and see if it frees up the suspension further.
Note that after setting the tire pressures, run them to get the tires up to temp. It could be that the sumis are just finished due to age. Mine worked pretty well for about 4 years prior to the rears going due to center wear. There will be a noticeable change when they warm.
-1º camber, 1/16" toe in with the driver installed. First click on the dampers (maybe). Steering response should be quick and linear with strong caster return. Front bar (factory type) set with the adjuster about one inch back from the end of the bar.
Front suspension should be free when bounced. Try loosening the bolts slightly and see if it frees up the suspension further.
Note that after setting the tire pressures, run them to get the tires up to temp. It could be that the sumis are just finished due to age. Mine worked pretty well for about 4 years prior to the rears going due to center wear. There will be a noticeable change when they warm.