Tyre skip/jump (Or can tyres be too wide?)

[daveenty]

I wasn't sure where to post this, was going to put it HERE but as it's not Mercedes related, it's probably safer in this forum.

1970 Ford Ranchero, Torino based. Big block V8 (heavy) with a steering box, not rack.

The truck's fitted with 7.5" x 15" rims on the front and currently shod with 235/60/15 Cooper Cobra tyres which are admittedly not exactly a premium make. All steering joints have been replaced where necessary, bearings are good with no visible play, shocks are new and it's been aligned on a Hunter machine, all less than 1,000 miles ago.

I fitted these tyres when I first got it a couple of years ago and have never really been happy with them. They are the same size as the Goodrich ones they replaced but I'm wondering if they're actually a bit too wide? According to a WEBSITE I often refer to for checking stuff like this, they're pretty much in the middle of what's acceptable for my rims, though I'm not convinced. I've tried them at varying pressures but they're still pretty much the same.

Every right hand bend feels like a challenge at the moment, with an awful amount of tyre skipping/jumping and a tendency to understeer towards the kerb. Obviously this can be controlled to a degree by the speed I approach them but I noticed last week that the tyre jumping was happening even when shunting around a yard, which made me think that a smaller tyre both in width and profile may help with this, both in reducing the footprint and having the added bonus of lowering the front which is still needed. Were I to go with a 205/50/15 tyre, which is still acceptable for my rim width then, according to the TYRE SIZE COMPARISON site, it would have the effect of reducing the width by just over an inch and the height by around three inches which would suit the aesthetics.

Incidentally, I mentioned right hand bends above as this is where the jumping seems to happen. Left handers are nowhere near as bad for some reason.

Any suggestion/advice appreciated.

 

[peterws1957]

I wasn't sure where to post this, was going to put it HERE but as it's not Mercedes related, it's probably safer in this forum.

1970 Ford Ranchero, Torino based. Big block V8 (heavy) with a steering box, not rack.

The truck's fitted with 7.5" x 15" rims on the front and currently shod with 235/60/15 Cooper Cobra tyres which are admittedly not exactly a premium make. All steering joints have been replaced where necessary, bearings are good with no visible play, shocks are new and it's been aligned on a Hunter machine, all less than 1,000 miles ago.

I fitted these tyres when I first got it a couple of years ago and have never really been happy with them. They are the same size as the Goodrich ones they replaced but I'm wondering if they're actually a bit too wide? According to a WEBSITE I often refer to for checking stuff like this, they're pretty much in the middle of what's acceptable for my rims, though I'm not convinced. I've tried them at varying pressures but they're still pretty much the same.

Every right hand bend feels like a challenge at the moment, with an awful amount of tyre skipping/jumping and a tendency to understeer towards the kerb. Obviously this can be controlled to a degree by the speed I approach them but I noticed last week that the tyre jumping was happening even when shunting around a yard, which made me think that a smaller tyre both in width and profile may help with this, both in reducing the footprint and having the added bonus of lowering the front which is still needed. Were I to go with a 205/50/15 tyre, which is still acceptable for my rim width then, according to the TYRE SIZE COMPARISON site, it would have the effect of reducing the width by just over an inch and the height by around three inches which would suit the aesthetics.

Incidentally, I mentioned right hand bends above as this is where the jumping seems to happen. Left handers are nowhere near as bad for some reason.

Any suggestion/advice appreciated.

Ah yes the handling of early US stuff. Part of the problem on early pickups is the heavy weight on the front end with relatively light weight on the rear. Cooper Cobras were the go to in the 70's and 80's along with BF Goodrich and were never known for handling capabilities, but I don't know if the rubber mix is the same as it was. Also 7.5" rims seem wide on the front, are they oem width and offset? Might be worth checking. If the Ranchero has coil springs it might be an idea to replace with uprated ones along with uprated shocks, depends how far you want to go since there are a lot of variables involved. Otherwise it's a case of putting up with the sometimes rather "exciting" ride early Yanks can give you. I'm sure there will be a Ranchero forum somewhere on the net which will provide some guidance though.

 

[daveenty]

Thanks Pete, was hoping you'd see this.

OEM rims were between 5J - 6J with a 14" diameter depending on trim level. Mine now has centerline drag alloys which are considerably larger The rears are bigger still at 10" x 15". Still can't get traction though, as you say above, it's very light on the back end.

It does have coils at the front but I'm reluctant to change them out as there are that many different part numbers I'd be concerned about getting the ride height and spring ratings correct as the thing's been modified that much. A local spring company have offered to remake them but they want them for up to 8 weeks, which isn't going to happen. The shocks are new and "heavy duty" as supplied by Rock Auto.

My (probably flawed) logic is that by reducing the footprint and using a better tyre brand I may be able to reduce this skipping a bit or at least stop it "tram-lining".

Oh and yes, there is a Ranchero forum, I've been all over it like a rash.

 

[peterws1957]

Thanks Pete, was hoping you'd see this.

OEM rims were between 5J - 6J with a 14" diameter depending on trim level. Mine now has centerline drag alloys which are considerably larger The rears are bigger still at 10" x 15". Still can't get traction though, as you say above, it's very light on the back end.

It does have coils at the front but I'm reluctant to change them out as there are that many different part numbers I'd be concerned about getting the ride height and spring ratings correct as the thing's been modified that much. A local spring company have offered to remake them but they want them for up to 8 weeks, which isn't going to happen. The shocks are new and "heavy duty" as supplied by Rock Auto.

My (probably flawed) logic is that by reducing the footprint and using a better tyre brand I may be able to reduce this skipping a bit or at least stop it "tram-lining".

Oh and yes, there is a Ranchero forum, I've been all over it like a rash.

It was a weird choice wasn't it for 14" rims - my Chevy has them. I'm sure your on the right line though by reducing the foot print on the front. If you have a front disc brake conversion you need to be careful of clearance obviously. Centerlines were my favourite wheel back in the day. Other than that it would be a case of messing with the geometry of the front suspension which can be a never ending rabbit hole.

 

[00slk]

You have a normal handling American car on wide tyres Dave

 

[daveenty]

It was a weird choice wasn't it for 14" rims - my Chevy has them. I'm sure your on the right line though by reducing the foot print on the front. If you have a front disc brake conversion you need to be careful of clearance obviously. Centerlines were my favourite wheel back in the day. Other than that it would be a case of messing with the geometry of the front suspension which can be a never ending rabbit hole.

I've had a chat with a couple of tyre places, National were very helpful though obviously won't commit to suggesting anything apart from an extremely minor size difference which is not really what I want. He did however suggest that to save money it may be worth trying a pair of part worn on the front to confirm suitability though stressed that they couldn't help me here with either supply or fitting. A sensible suggestion which I thanked him for so I'm now trying some of the local independent tyre shops who do this sort of thing before wandering over to the bay of dreams to widen my search. I won't be changing the rims so the discs shouldn't be affected though they were factory on the big blocks as it happens.

You have a normal handling American car on wide tyres Dave

Which will hopefully soon be a normal handling American car on narrower tyres Pete.

 

[EmilysDad]

I've had a chat with a couple of tyre places, National were very helpful though obviously won't commit to suggesting anything .....

I asked them for a price for an exhaust for Emilys the Seciento ... they were dearer than the main dealer.
I tend to use Radcliffe Moor Road for tyres ..... they've been there for years.

 

[daveenty]

I asked them for a price for an exhaust for Emilys the Seciento ... they were dearer than the main dealer.
I tend to use Radcliffe Moor Road for tyres ..... they've been there for years.

Yes, I remember you mentioning them before Andy. I may have a chat with them but I'm only after advice and/or suggestions at the moment as I'm not in a rush to commit to anything as yet.

Incidentally, I don't know if you're aware but John at JBM is retiring at he end of this month.

 

[EmilysDad]

Incidentally, I don't know if you're aware but John at JBM is retiring at he end of this month.

oh no!
Where will I take my car to now?

 

[00slk]

I've had a chat with a couple of tyre places, National were very helpful though obviously won't commit to suggesting anything apart from an extremely minor size difference which is not really what I want. He did however suggest that to save money it may be worth trying a pair of part worn on the front to confirm suitability though stressed that they couldn't help me here with either supply or fitting. A sensible suggestion which I thanked him for so I'm now trying some of the local independent tyre shops who do this sort of thing before wandering over to the bay of dreams to widen my search. I won't be changing the rims so the discs shouldn't be affected though they were factory on the big blocks as it happens.



Which will hopefully soon be a normal handling American car on narrower tyres Pete.

I'm sure I've got some motorcycle tyres here Dave.........I'll close the door after me......

 

[Blobcat]

I'm sure I've got some motorcycle tyres here Dave.........I'll close the door after me......

I’ve a few lying around as well in various widths and construction… 5 crossplies in that pile…

 

[00slk]

I’ve a few lying around as well in various widths and construction… 5 crossplies in that pile…

View attachment 90776

Hoarder......