Wheel and tire numbers

[Bendder]

I think this will spark some debate as I know some don't like bigger wheels but I kind of do so this is what I have found. So, do any of you think they would fit? I have not measured for backspace so this is where I need some oppinions. I think the amount beyonde the mounting face should be OK but again oppinions are welcome.

17x7 +40 front wheel and tire set

7 x 25.4 = 177.8 / 2 = 88.9 – 40 = 48.9 beyond mounting face 4.05mm more than stock
7 x 25.4 = 177.8 / 2 = 88.9 + 40 = 128.9mm backspace (5.074â€￾) 1.34â€￾ more
PROXES T1R by Toyo
215/40ZR17** 87W BW 280AA A 10 23.8dia
8.7sec 11.1slr 543 7.5 7.0-8.5wheel

tire dia 603.8-589.2=14.6mm larger than stock

17x8 +50 rear wheel and tire set

8 x825.4 = 203.2 / 2 = 101.6-50=51.6 beyond mounting face 6.75mm more than stock
8 x825.4 = 203.2 / 2 = 101.6+50=151.6mm backspace (5.97â€￾) 2.236â€￾ more
PROXES T1R by Toyo
245/35ZR17 87W BW 280AA A 10 23.8dia
9.6sec 11.1slr 543 8.5 8.0-9.5wheel

tire dia 603.3-589.2=14.1mm larger than stock





stock

13 x 5.5 +25

5.5 x 25.4 = 139.7 / 2 = 69.85 – 25 = 44.85 beyond mounting face
5.5 x 25.4 = 139.7 / 2 = 69.85 + 25 = 94.85mm backspace (3.734â€￾)


Mark
1977 TR7 FHC
1978 TR7 FHC
1980 TR7 DHC
1980 Rover SD1 4.0L

[PeterTR7V8]

Just bear in mind that the lower profile your tyres have, the worse the car will handle & feel.


Never say die. At least not while you're still breathing.

[Bendder]

Just to put things in perspective, I have been talking with a coil spring producer and have sent them both a front and rear spring to take all the measurments they like. Peter, yes I understand that ride will be affected and so that is why I am talking with the spring manufacturer. As for making it handle worse, I think if planned well there is no reason it should not improve. Granted if all I were to do was throw on a set of 17's I would agree it would probably not be prety ! What we are talking about so far is going with a variable rate at both the front and rear. The numbers have yet to be determined as the springs need to be evaluated first and I need to get some weight measuments at each corner to give them an idea of how much weight the springs are carrying obviously less wheel tire and strut assembly weights as it does not actualy carry those. The reason for variable rate is to get the ride back to being comfortable but still have the ability to push up against a higher rate as in conering. The one draw back of the variable rate is that it takes an inch or two to get into the higher rate portion of the spring. This means that you get a bit of roll before it sets. Some of this can be down played by the anti roll bars but it will still happen. So this is where I am at right now it's realy all about the numbers at this time and see if it can all be figured out.

There are some other nagging questions in my minde after having read some posts latly also. Regarding wheel diameter versus the PCD and not exceeding a given size ie:14 or 15 I believe it was.

Here is my take on it. If the section width was not changed and your lateral grip was no diferent, then wheel diameter would make no difference so long as overall tire diameter was the same. Now if you changed the tire section width and increased the amount of lateral force neeeded to break the tire loose then you would be increasing the sheer force on the threads of the wheel studs...so they could possibly sheer. Again wheel diameter plays no roll if tire dia is still constant. so if you could calculate the increase in lateral force (i have no idea how. My math skills are not that advanced) you could calculate the additional amount of sheer force to the threads on the mounting studs and do one of a few things to fix it. One would be to go to a higher grade stud with more force needed to sheer the threads. Go to a larger stud diameter which would account for more thread length due to diameter which in turn gives you greater sheer force required. And finnaly I think the simplest solution. Sread the load over more threads on the same or just longer stud by using a deeper nut.

This is all just stuff going through my head so if anyone can fault my thinking, please do i am interested in what you have to say.

Mark
1977 TR7 FHC
1978 TR7 FHC
1980 TR7 DHC
1980 Rover SD1 4.0L

[Hasbeen]

Mark, somewhere I have a photo of a 1967 Brabham Repco, F1 racing
car, I was driving in 68, going around a 100 MPH corner. In this
shot it has Firestone racing tyres on it.

Firestones, of that era, had reasonably stiff side walls, & were
designed for the Ferrari, & Lotus F1s, which had very little camber
change due to suspension movement, or body roll.

Dunlop, & Goodyear racing tyres had softer, more flexible,
sidewalls, & were much better suited to the Brabham, which had
quite a bit of camber change. Unfortunately for me, Firestone
offered my cars owner a much better contract, that year.

Racing tyres still had tread in those days, & in this photo, I have
3 of the 7 bars of tread, on the front inside wheel off the track,
& 4 of the 8 bars of tread, on the rear inside wheel off the
track. Not the best system for maximum grip.

The thing was a bit of a bitch, on those tyres, not all that much
slower, but bloody soggy on turn in, at lower speeds, [under 85
MPH], & far too easy to get into tyre destroying power slides, at
the exit.

In one race I had a blow out, of a front tyre. When I got back to
the pits, the crew did not have a front there, they were in the
truck. The owner of a sister car, in the next pit, rolled a
Goodyear shod front wheel over to them, which they fitted, & off I
went. [Oz motor racing was like that back then].

I was 1.2 seconds a lap quicker, with that one Goodyear, than
before. This was not because the Goodyear was a better tyre than
the Firestone, but because the Goodyear had been designed for
Brabham, & suited the suspension.

Think about it, before you spend a lot of money.

I find my 7, with it's 13s is a faster car than my 8, with it's
lower profile 15s, on all our country roads. The tyre allows the
car to ignore the bumps & waves in our roads, where the 8 is qiute
unsettled by the larger imperfections.

What you plan, may be great, but with stiff sidewall low profile
tyres, on a car with lots of camber change, it could easily be a
waste of money. If you go ahead, try to find which of the low
profile tyres has the most flexible side wall. That should be the
most suitable tyre for an 8

Hasbeen

[Bendder]

hummm camber... I see your point and had not thought about that. Being that are cars have no camber adjustment It is definatly something to add in to the to do list to make something like this work to its potential. Can't remember who off the top of my head right at the moment but I know there are a couple kits out there to allow addjustment. this would be more important seeing as the lower profile would be more suseptible to change in camber resulting from say a different ride height. I think the minimal amount in change to camber should be acceptable in straight line driving and not affect things to much on a flat road but like you say on a say a rutted road that camber change as the vehicle nose moves up and down may prove to guide the car more aggrssivly up or down the rut causing it to lurch side to side. I still think that regardless of diameter of wheel that there is no reason why things can't be improved upon its just a matter of identifiing the problem areas and seeing if they can be resolved and preferrably improved upon. This is a long term sort of project thatReally when you think about it is not the kind that should cost huge ammounts of money. The springs are probably the cheapest part of the whole idea and the wheels regardless of type or size, the most expensive. I suppose no mater what wheel and tire combination anybody chosses that is not stock the resulting affect of suspension and how it will affect the car should be addressed, unfortunatly not that many people see it that way. I have had a few people say "don't worry about it it will be fine" ??hummm... then there is the other side of the bunch that will say "your wasting your time with all that stuff" but is'nt that what a hobby is about? wasting some time and pusuing something you actualy have an interest in?

BTW Hasbeen. They are calling for between 15-20cm of snow here tomorro. Guess you won't be having that in your neck of the woods!

Mark
1977 TR7 FHC
1978 TR7 FHC
1980 TR7 DHC
1980 Rover SD1 4.0L

[Beans]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Bendder</i>

... you would be increasing the sheer force on the threads of the wheel studs...so they could possibly sheer ... <hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
I wouldn't worry about that, haven't experienced or heard of the original studs shearing of.

[quote]<i>Originally posted by Bendder</i>

hummm camber... but like you say on a say a rutted road that camber change as the vehicle nose moves up and down may prove to guide the car more aggrssivly up or down the rut causing it to lurch side to side ... <hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
From own experience I can tell that on rutted and bumpy roads, the lower the tyre wall is the more nervous the car will be. This also depends on the road surface and is often “highlightedâ€￾ under braking, (caused by the suspension geometry changes).

Nothing to add to Hasbeen’s remarks [;)]
I am actually thinking of changing the wheels for the DHC from 15" back to 13" [:)]

<center>
<font color="blue"><i>1981 TR7 FHC Sprint (better known as 't Kreng)
1980 TR7 DHC (my first car currently being restored)
In parts a 1980 TR7 PI DHC, 1981 TR7 DHC, 1981 TR7 FHC</font id="blue">
<font color="red">http://tr7beans.blogspot.com/</i></font id="red"></center>

[PeterTR7V8]

KMac make a good camber kit which is reasonably priced. The thing with having a finely tuned suspension on a road car is that it will only work at its optimum on a particular surface whereas public roads vary widely in quality & type.


Never say die. At least not while you're still breathing.

[Hasbeen]

Yes Mark, it's damn hot here at present, getting up towards 40 C in
some areas.

Yesterday I put the hood up on the 8, for the first time in 7
months. It was just too hot to go topless. After half an hour
parked in the sun, the bonnet, [engine hood] was too hot to touch.

Beans, I would think about 13s on the 8, if they would fit over the
brakes.

AS the city moves out to engulf us, [a 50,000 people satellite city
to be built 7Km from us] they are upgrading the major roads. As
they do this they straighten then, so on the smooth roads you would
have to drive at double the speed limit, to have any fun. The back
roads get rougher, due to neglect.

Anything that goes up a mountain, & is twisty, is now restricted to
60Km. This is to protect the sunday tourist from himself. They tend
to run off the road, when the tomato falls out of the sandwich in
their right hand, because they have trouble picking it up with the
left hand. That's the one with the can of Coke in it.

Hasbeen

[PeterTR7V8]

The perils of low profile tyres... [:D][:D][:D]



Never say die. At least not while you're still breathing.