# [EVDL] Different Tires, Different Pressures?



## EVDL List (Jul 27, 2007)

In an effort to improve the Wh/mile, I decided to pump up the tires to close to maximum. When I looked at the tires, though, I discovered that the front tires were different from the rear ones, and have different max psi. Is it okay to have the front tires at a different psi than the rear, or should I inflate them all to the same psi?

Thanks.

Bill

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## EVDL List (Jul 27, 2007)

Hello Bill,

The maximum psi tire pressure is rated for a maximum load rating.

For example, if you have a actual load rating of 1000 lbs on a tire that has 
a maximum load rating of 1000 lbs at 40 psi, then apply 40 psi air pressure 
to that tire. It is not a good ideal to have 1000 lbs on a tire that has a 
load rating of 1000 lbs. This may be ok if the vehicle is not moving. A 
moving vehicle cause forward and rearward thrust that causes increase weight 
on the tire. Sometimes the tire specifications may the thrust rating 
engineer for a tire that may be 125 to 150 percent over the load rating of 
the tire for normal driving.

Ok, lets say the rear axil weight is 2000 lbs on a scale, this means each 
wheel and tire has 1000 lbs load on it. Pick out a tire that has a load 
rating of 1000 lbs or if does not have a listed thrust rating, than at least 
a 1250 to 1500 rating tire. Apply the psi air pressure for 1000 lbs at 40 
psi with the tire jack off the grade. Lower the tire until it just contacts 
the road surface. Measure from the road surface to the bottom rim of the 
wheel. Lower the vehicle completely where all the weight is on the tire and 
measure again. A preferred reading in inches is between 0.375 to 0.500 of a 
inch.
This is call the deflection rate of the tire.

Do the same for the front tires and adjust the tire psi until the deflection 
rate is the same.

I am running a LRR tire that has 2 ply side walls and a very stiff 2 by 2 
face. The side walls in a LRR tire takes up the deflection which keeps the 
face of the tire rounder. My tire specifications was for a 7150 lb EV that 
had a tire rated for 65 psi at a load rating of 2350 lbs and a thrust rating 
of 3500 lbs. The wheels are also rated for 3500 lbs and a new axil and 
bearing set is rated for 4000 lbs.

I air up the tires to 65 psi with a 0.50 inch side wall deflection rate, 
which made it a rough ride on very rough roads. I reduce the EV weight to 
6800 lbs (with the driver) and reduce the air pressure to 52 PSI for a 0.5 
inch deflection rate. The front of the EV which weighs less than the rear, 
now has 38 PSI instead of 50 PSI.

You have to adjust the psi air pressure, so the deflection rate is the same 
for all the tires. My AH per mile have not change where I cannot tell the 
difference.

Roland



----- Original Message ----- 
From: "Bill Dennis" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, May 15, 2012 1:24 PM
Subject: [EVDL] Different Tires, Different Pressures?


> In an effort to improve the Wh/mile, I decided to pump up the tires to 
> close to maximum. When I looked at the tires, though, I discovered that 
> the front tires were different from the rear ones, and have different max 
> psi. Is it okay to have the front tires at a different psi than the 
> rear, or should I inflate them all to the same psi?
>
> Thanks.
>
> Bill
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere. Thanks.
> |
> | REPLYING: address your message to [email protected] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
> 

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to [email protected] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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## EVDL List (Jul 27, 2007)

It is OK to have the front different from the rear, but both front should
be the same and not exceding the max pres marked on theos tires. similarly
the two rear tires should have the same pressure and not exceed the max
pres marked on those tires. after you increase tire pressure you should
observe the wear pattern and if the tires are wearing in the center more
than on both edges the pressure is too high for your vehicle weight and
vice-versa if the edges are both wearing and the center is wearing less the
pressure is too low for your load. if only one edge is wearing that is an
alignment problem. The recomended tire sressure from the manufacturer of
the vehicle is with original liad characteristics, and may be different on
a conversion.
Regards,
*Dennis Lee Miles*

++++++++++++++++++++++++++++++++++++++++++++++++



> Bill Dennis <[email protected]> wrote:
> 
> > In an effort to improve the Wh/mile, I decided to pump up the tires to
> > close to maximum. When I looked at the tires, though, I discovered that
> ...


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## EVDL List (Jul 27, 2007)

I believe I read on one of the Prius hypermiling sites that rear (54) should be higher than front (52).

Remember, this advice is worth what you paid for it ( unless you pay for Internet by the bit, in which case it could cost you)
John




> Dennis Miles <[email protected]> wrote:
> 
> > It is OK to have the front different from the rear, but both front should
> > be the same and not exceding the max pres marked on theos tires. similarly
> ...


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## EVDL List (Jul 27, 2007)

Very few vehicles require equal front / rear tire pressures because 
the front / rear weights of very few are equally balanced.
Look inside the fuel filler flap of any Mercedes Benz and you'll see 
a chart recommending lower pressures in the front tires than in the 
rear tires.

Al


At 01:58 PM 5/15/2012, JOHN OCONNOR wrote:
>I believe I read on one of the Prius hypermiling sites that rear 
>(54) should be higher than front (52).
>
>Remember, this advice is worth what you paid for it ( unless you pay 
>for Internet by the bit, in which case it could cost you)
>John
>
>
>


> Dennis Miles <[email protected]> wrote:
> >
> > > It is OK to have the front different from the rear, but both front should
> > > be the same and not exceding the max pres marked on theos tires. similarly
> ...


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## EVDL List (Jul 27, 2007)

> On 15 May 2012 at 16:58, JOHN OCONNOR wrote:
> 
> > I believe I read on one of the Prius hypermiling sites that rear (54) should
> > be higher than front (52).
> ...


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## EVDL List (Jul 27, 2007)

AFAIK, the Prius has higher pressure in the front though it may
have changed for later models.
My 2002 has (from memory) 34 PSI front and 32 PSI rear as
manufacturer recommendation, because the front weight is
slightly larger with the front engine and transaxle.
Many hypermilers use 51 PSI tires and pump them close to
the max sidewall cold pressure - I was running them near
47 front, 45 rear and saw a nice even wear and low resistance
(instead of wearing the edges of the thread off the tires 
and a softer but higher resistance ride)

I have no experience with later models though, but in
general the tire pressure varies with the surface of
the contact patch (tire width) and weight on each tire.

Success,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of EVDL Administrator
Sent: Wednesday, May 16, 2012 11:24 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Different Tires, Different Pressures?



> On 15 May 2012 at 16:58, JOHN OCONNOR wrote:
> 
> > I believe I read on one of the Prius hypermiling sites that rear (54)
> > should be higher than front (52).
> ...


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## EVDL List (Jul 27, 2007)

When I was racing solo I/II we would make a line on the tire from the
sidewall down into the tread with white shoe polish and then set the
tire pressure so that the line would be worn from the tread but not from
the sidewall. Each time the tire pressure was changed the line would be
re-drawn. This was done on all tires.

I don't know if this works as well on the street, we would get quite a
lot of roll-over on the front tires on front-drive cars and I remember
having something like 45 lbs pressure in the front and 20 in the rear as
normal for racing conditions (which was adjusted back to 30 all around
before leaving the track).



> On 12-05-16 02:24 PM, EVDL Administrator wrote:
> > On 15 May 2012 at 16:58, JOHN OCONNOR wrote:
> >
> >> > I believe I read on one of the Prius hypermiling sites that rear (54) should
> ...


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## EVDL List (Jul 27, 2007)

Why would you adjust it back to 30 before leaving the track, if 45/20 was
optimal for the car?

Brett



> Paul Wujek <[email protected]> wrote:
> 
> > When I was racing solo I/II we would make a line on the tire from the
> > sidewall down into the tread with white shoe polish and then set the
> ...


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## EVDL List (Jul 27, 2007)

Because it was optimal for the tight track courses, not necessarily for
the road.

For example the low rear tire pressure would cause problems with any
passengers, but was great for improved handling in hairpin corners.



> On 12-05-16 04:01 PM, Brett Davis wrote:
> > Why would you adjust it back to 30 before leaving the track, if 45/20 was
> > optimal for the car?
> >
> ...


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