Different Tires and camber requirements

[turbogrill]

Hi,

 

I have run a few sessions with the CR-1 but I am not able to get the same speed as I did with the re71r. 

 

Looking at the data I am a few mph slower in tight corners with the CR-1 than the RE71r.  Based on internet facts they should be very similar. The CR-1 is a little wider than re71r (both 255s).

 

When I look at it the inner part of the tire looks brand new but the outer part is starting to look a little worn. My car setup is pretty soft (street springs and sway).

Could it be that the CR-1 requires more camber?  And if so why?

 

(Ordered a pyrometer to test with)

[wvumtnbkr]

The simple answer is that yes, it m8ght want different alignment or pressures.

 

The reason why is: construction of the tire.

 

There's a bunch of variables that go into building a tire.  Compound and tread pattern are the most obvious, but construction can be different enough that it will want more or less camber or pressures due to sidewall stiffness.

[Ian]

Different tires flex in different ways.  The alignment settings that work well with one tire, may not with another.  Carcass flex, tread squirm, compound temperature all play a roll.

 

If you're wearing one part of the tire and not another, you're likely not using the whole contact patch.

[turbogrill]

I softened up the front with a smaller sway, car drives much better now. 

 

But it does roll a little more, would stiffen up the front and rear help maybe.

 

Hard to get more camber without points...

[collinskl1]

11 hours ago, Ian said:

Different tires flex in different ways.  The alignment settings that work well with one tire, may not with another.  Carcass flex, tread squirm, compound temperature all play a roll.

 

If you're wearing one part of the tire and not another, you're likely not using the whole contact patch.

 

First part is on target - like Rob said, tire constructions vary and getting maximum lateral grip from different tires can take different car setups.

 

Second part is less correct. The "contact patch" (we call it footprint) is the only part of the tire that touches the ground, and it moves and changes shape dynamically as the car transfers weight around. By definition, the tire wears from where the footprint is, and only from the footprint... so if you're not wearing the whole tire evenly, your footprint is also not using the whole tire evenly. That could mean (and usually does for our use cases) that the static footprint is narrower than the tread width of the tire, and through a turn the footprint "moves" from the inside shoulder of the tire to the outside.

 

From the OP's description of unworn inside shoulders and overworn outside shoulders, you're not using the inside shoulder of the turn under the high load high slip angle maneuvers (turns), and those high contact pressures with the ground are wearing the outer shoulders faster because the inside shoulders are likely not in contact with the track. Sounds like you need more camber.

[MR2 Biohazard]

14 hours ago, turbogrill said:

Hi,

 

I have run a few sessions with the CR-1 but I am not able to get the same speed as I did with the re71r. 

 

Looking at the data I am a few mph slower in tight corners with the CR-1 than the RE71r.  Based on internet facts they should be very similar. The CR-1 is a little wider than re71r (both 255s).

 

When I look at it the inner part of the tire looks brand new but the outer part is starting to look a little worn. My car setup is pretty soft (street springs and sway).

Could it be that the CR-1 requires more camber?  And if so why?

 

(Ordered a pyrometer to test with)

Did you take tire temps right after a hot session with as little cool down at possible? If no, that is the first thing to do. Tire temps across the tire are really what matters and will tell you how to setup the suspension. If you do not have that you are really guessing and just hoping.

 

The other idea I see that says guessing also is "What tire pressure do you run?" One car can it can be 23psi to get the correct tire temperatures and grip and another be 39psi on the same tire on a different car. Even on the same type of cars, different springs, shocks, balance, ect. Each car is really different. It can be different and different driving styles and aggression can have you adjust. Also, cold pressure to hot pressure.

 

I have a really nice tire temp and pressure gauge. If you are at the track the same day as me, come find me and I will let you use it or can come and do it when you have a pit stop. It really does make a world of difference. That offer goes to anyone who wants to give it a try, just find me at the track and do not be shy, ask. I also have scales I bring if anyone wants to cornerbalance prior to the race.

[turbogrill]

Thanks! I appreciate the offer!

I am always alone at our local track, so taking tire temps is a little difficult. How long do you think it takes for a tire to cool down?

I think I can measure the tire within 45s (with the risk of getting overrun by other Miatas ).

[MR2 Biohazard]

6 minutes ago, turbogrill said:

Thanks! I appreciate the offer!

I am always alone at our local track, so taking tire temps is a little difficult. How long do you think it takes for a tire to cool down?

I think I can measure the tire within 45s (with the risk of getting overrun by other Miatas ).

I do it myself, you just need to plan for it. I do some really hots laps and push at the end, come in to the pit lane, stop, jump out, grab my pyrometer from the wall and do the temps. It takes like 30 seconds to take them. On mine I just hit the button and it saves it, then I can review later. If you do this you will have great readings and get it right.  It is the one below.

 

https://competitionmotorsport.com/longacre-temperature-compensated-tire-pressure-gauge-0-100-psi?utm_source=google&utm_medium=cpc&utm_campaign=shopping&gclid=CjwKCAjwj8eJBhA5EiwAg3z0mzfHS3SxTEx9i7sTAYpt4GuhGbkHxVo13T4hJPdHnb4O6IKUawBBhRoC7IAQAvD_BwE

[turbogrill]

7 minutes ago, MR2 Biohazard said:

I do it myself, you just need to plan for it. I do some really hots laps and push at the end, come in to the pit lane, stop, jump out, grab my pyrometer from the wall and do the temps. It takes like 30 seconds to take them. On mine I just hit the button and it saves it, then I can review later. If you do this you will have great readings and get it right.  It is the one below.

 

https://competitionmotorsport.com/longacre-temperature-compensated-tire-pressure-gauge-0-100-psi?utm_source=google&utm_medium=cpc&utm_campaign=shopping&gclid=CjwKCAjwj8eJBhA5EiwAg3z0mzfHS3SxTEx9i7sTAYpt4GuhGbkHxVo13T4hJPdHnb4O6IKUawBBhRoC7IAQAvD_BwE

 

Thanks!

 

Funny, last week I spent 2 hours trying to setup my car using an inaccurate tire pressure gauge. It kinda sucked.

 

 

[turbogrill]

I also put on a set of half used NT01, the car turned into an understeering minivan and would need some adjustments.

 

Either that proves the point on how much tires affect the characteristics of the car or the tires where just done.

 

 

[collinskl1]

13 minutes ago, turbogrill said:

I also put on a set of half used NT01, the car turned into an understeering minivan and would need some adjustments.

 

Either that proves the point on how much tires affect the characteristics of the car or the tires where just done.

 

 

Well, it's likely both of those combined with the fact that NT01s are pretty poor to begin with.

[Grant]

On 9/2/2021 at 5:24 PM, turbogrill said:

Looking at the data I am a few mph slower in tight corners with the CR-1 than the RE71r.  Based on internet facts they should be very similar. The CR-1 is a little wider than re71r (both 255s).

Can you post the data? Or a screenshot of it? A few mph in a lower corner is a lot, and probably not something that can be made up with a camber change (assuming you're fairly close to optimal camber).

 

Temps are helpful to quickly get camber in the ballpark, but to actually find the optimal settings you'll need to experiment and use daq or lap times.

Edited September 3, 2021 by Grant

[mender]

10 hours ago, turbogrill said:

I also put on a set of half used NT01, the car turned into an understeering minivan and would need some adjustments.

 

Either that proves the point on how much tires affect the characteristics of the car or the tires where just done.

 

 

I'm assuming that you put them on the front. That will definitely affect the handling and make it hard to assess suspension adjustments. 

 

Best to either use a new or at least matched set for testing. Next best is if you have to use a pair of older/used tires, put the pair on one side of the car instead of the front or back. That way the balance is much less affected, and you can even do grip comparisons left to right.

 

 

Edited September 4, 2021 by mender

[turbogrill]

16 hours ago, Grant said:

Can you post the data? Or a screenshot of it? A few mph in a lower corner is a lot, and probably not something that can be made up with a camber change (assuming you're fairly close to optimal camber).

 

Temps are helpful to quickly get camber in the ballpark, but to actually find the optimal settings you'll need to experiment and use daq or lap times.

 

I have heard similar things on Facebook where they are 1s or so slower on CR-1 than RE71rs. However I have also read that the CR-1 is about the same speed as A052. GRM did a test where CR-1 and RT660 where on par. 

 

So not sure what to take from it.

The fastest lap time we have ever had has been on re71r, that can be due to many factors. Also for the below data CR-1 was in Aug and RE71r in April. Augusti tends to be hot in Texas. So not a scientific test by any means

 

I will continue to try and improve with CR-1, will do a proper pyrometer check as well. Maybe we got lucky with the re71r was just setup perfectly but the CR-1 needs some tweak. 

 

 

 

 

 

[Grant]

1 hour ago, turbogrill said:

 

I have heard similar things on Facebook where they are 1s or so slower on CR-1 than RE71rs. However I have also read that the CR-1 is about the same speed as A052. GRM did a test where CR-1 and RT660 where on par. 

 

So not sure what to take from it.

The fastest lap time we have ever had has been on re71r, that can be due to many factors. Also for the below data CR-1 was in Aug and RE71r in April. Augusti tends to be hot in Texas. So not a scientific test by any means

 

I will continue to try and improve with CR-1, will do a proper pyrometer check as well. Maybe we got lucky with the re71r was just setup perfectly but the CR-1 needs some tweak. 

 

 

What daq is that? If it can export to VBO format I can take a closer look.

 

However the cornering speed differences look like driving differences to me, since the tires are clearly making more-similar amounts of grip in other parts of the track. All other things equal, going from 43.2 to 46.2 mph is a 14% increase in grip; absolutely massive. However your exit speed on the CR-1s is higher, which tells me a lot of the vmin drop is probably because you took a later apex.

 

In situations like these I usually try to isolate one corner I know I'm always taking as fast as possible on both tires.

 

Of course the car is also accelerating faster in April.

[turbogrill]

Could be!

 

Maybe they behave differently and that's is why. I have had maybe 8 sessions in a different car between these two sessions, so might have improved. (But with slower lap time due to whatever reason)

 

Got a race 25-26, majority of other cars are on RS4s since they are 15" wheels.

Can get a better understanding then.

 

(no body seem to know they make cr1 in wide 15")

 

I just want a drop in replacement for re71r! 8 tires would last a race weekend and also plenty of practice. Good in wet and easy for beginners to drive.

(Harris Hill always have 2-3 hours wet, so about 10h dry max speed)

 

 

 

 

[turbogrill]

Other internet people are having the same issues as me, they need much more camber with CR-1 than RE71r. CR-1 has super soft sidewalls.

 

From a champcar perspective that might be bad since getting camber cost a lot of points.

[mender]

https://www.liveabout.com/how-cambered-tires-work-3234468

[TKRiggs]

On 9/2/2021 at 5:24 PM, turbogrill said:

The CR-1 is a little wider than re71r (both 255s)

My understanding is that your "wheel width" should be as wide to 1/2" wider than your tire tread width.  If the CR-1 is wider and you did not accommodate for this in your wheel selection, it will roll more....and yes...you'll have to make up for it with camber/tire pressures.  We've personally experienced this with A052s.  Once we went to a wider wheel (by .5") it cleaned up the slop (especially on entry) and became less camber dependent (that is to say we could run slightly less camber than before).  

Edited October 11, 2021 by TKRiggs
clarity of post

[jakks]

2 hours ago, turbogrill said:

Other internet people are having the same issues as me, they need much more camber with CR-1 than RE71r. CR-1 has super soft sidewalls.

 

From a champcar perspective that might be bad since getting camber cost a lot of points.

Go to a slightly wider wheel to stiffen up the sidewalls. We went from an 8” wheel to a 9” wheel with 225 RS-4’s. Same track, Warmer temps on 9” wheels and each driver picked up between 1.8 and 2 seconds. All in cornering speeds. Some upwards of 5mph. I contribute 0.5 or so of that to knowing the track better, but each driver said the car drove totally different.

[turbogrill]

Running 255s on a 17x10 rim. The CR-1 are a little wider then the RE71rs so maybe that can explain it. I think they make 245s I could try that maybe.

 

They make 18x10.5 for my car (NC Miata), but I don't think I want to go to 18". I also just spent a ton of money on new nice wheels

 

 

 

 

 

[Grant]

A 17x10 with 255s is plenty of wheel. At the Firm I went from 1:17.2 to 1:17.8 going from 255s on 17x10s to 225s on the stock 17x7 wheels. Straight line performance with the stock wheels was maybe a half a mph better, so fairly negligible. We're pretty close to maxed out on tires.

 

Wider wheels should help but 2 seconds from 1" of wheel increase is above and beyond anything I've ever seen. I would be thrilled to get 0.2s out of that. The wider wheel will feel crisper, which may help some drivers push harder? Too-low of tire pressure does something similar; the car feels like crap but can still be driven very close to as fast as it can with better pressures. Or maybe the 9" RS4s were cycled out. That's all I can think of.

Edited October 11, 2021 by Grant