Does anybody know how to work out what is the largest wheel/tyre combination that you can fit safely to any car without modifying or fitting spacers?

The reason I ask is that I have a set of Grizzly Claw Mud Terrain tyres for my Defender and as they are now 6 years old and a couple have several large bulges on the sidewalls (these tyres are remoulds) and I think that they are probably not safe for use on the road now when I drive 65 miles to get to off road events. They are great tyres but really carve up the ground and they are AWFUL for driving onroad so I'm thinking of buy a set of new BFG MTRs. Currently I also run with a set of BFG A/T KOs which are brilliant onroad and pretty good for most of the off roading I do - these are 265/75R16's the Grizllies are 15". At the weekend there was a guy running a heavily moded 90 with 35" BFG MTRs which looked like a set of balloons - but they are a bit extreme for what I want and also he had a huge suspension lift and extended wheelarches........ To fit the MTRs I'm going to have to buy a new set of wheels too so want to get the combination right. 2020 Pangea Green 1st Edition D240 New Defender 110 is here and loving it
2018 Melting Silver Mini Countryman PHEV - soon to be replaced
2015MY Corris Grey SDv6 HSE Dynamic, the best car I have ever owned, totally reliable only a cou0le of rattles in 3 years, now no longer in my care
Also in my garage is a 1996 TDi300 Defender 90 County HT made into a fake CSW

Tim i used to have a set of Grizzly claws and on a trip back down the motorway one of the tyres lost several of its big centre rubber treads, i ran my 90 on a set of 900x16's the same tyres as fitted to a 101 L/R they were huge and worked ok but made the 90 very very slow, but it did go any where,trouble is you needed a ladder to get into the dam thing and the 90 does have a 4"lift

I would say that the best people to talk to is the tyre supplier, or as i have done, trial and error, but it does work out expensive if it doesnt work  some of my Previous cars
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current vehicles
RRS 3.0 L494 Autobiography
Audi R8 V10 Spyder
AC Cobra
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Suzuki Jimney

Cheers Envoy, I do like the Grizzlies but they are not kind to the trails, I haven't had any problems with the lugs although some of my friends have and Bronco told them it was because they were running with the pressures less than 30psi and at speed on hard roads so the compound gets hot and they can de-laminate or loose the cleats. I doubt that BFG MTRs would be as good offroad but they are an awful lot nicer to run on the road on than Grizzlies! Also Grizzlies and rain on road isn't a fun combination! Braking................. what braking!  2020 Pangea Green 1st Edition D240 New Defender 110 is here and loving it
2018 Melting Silver Mini Countryman PHEV - soon to be replaced
2015MY Corris Grey SDv6 HSE Dynamic, the best car I have ever owned, totally reliable only a cou0le of rattles in 3 years, now no longer in my care
Also in my garage is a 1996 TDi300 Defender 90 County HT made into a fake CSW

Brakes, you dont need brakes when you are running on a set of Grizzly's you just drive over things

What i did find with them, it got a bit boring i never got stuck any where some of my Previous cars
--------------------------------
P38 Range Rover Autobiography
RRS 2.7 HSE Silver
RRS TDV8 HSE silver
FFRR Vogue black
Disco3 HSE silver
RRS 2.7 HSE silver
RRS 3.0 HSE BALTI BLUE
______________________________
current vehicles
RRS 3.0 L494 Autobiography
Audi R8 V10 Spyder
AC Cobra
Landrover Defender 90
Landrover Defender 110
Suzuki Jimney

I only use mine when I know the going is going to be very very wet, otherwise the AT's cope very well and give the boys who have winches something to do if I do get stuck.................... although this weekend I had to pull a couple of them out of the soft bits after they burned out their electric winches! 2020 Pangea Green 1st Edition D240 New Defender 110 is here and loving it
2018 Melting Silver Mini Countryman PHEV - soon to be replaced
2015MY Corris Grey SDv6 HSE Dynamic, the best car I have ever owned, totally reliable only a cou0le of rattles in 3 years, now no longer in my care
Also in my garage is a 1996 TDi300 Defender 90 County HT made into a fake CSW

Tim its always funny when the electric winches give up the ghost, you cant beat a good old fashioned mechanical pto driven winch that pulls the side of a house down  some of my Previous cars
--------------------------------
P38 Range Rover Autobiography
RRS 2.7 HSE Silver
RRS TDV8 HSE silver
FFRR Vogue black
Disco3 HSE silver
RRS 2.7 HSE silver
RRS 3.0 HSE BALTI BLUE
______________________________
current vehicles
RRS 3.0 L494 Autobiography
Audi R8 V10 Spyder
AC Cobra
Landrover Defender 90
Landrover Defender 110
Suzuki Jimney

When the 90 gets it's new chassis a MileMarker hydraulic winch is also on the "to do" list! 2020 Pangea Green 1st Edition D240 New Defender 110 is here and loving it
2018 Melting Silver Mini Countryman PHEV - soon to be replaced
2015MY Corris Grey SDv6 HSE Dynamic, the best car I have ever owned, totally reliable only a cou0le of rattles in 3 years, now no longer in my care
Also in my garage is a 1996 TDi300 Defender 90 County HT made into a fake CSW

Now thats even better than a manual winch Tim  some of my Previous cars
--------------------------------
P38 Range Rover Autobiography
RRS 2.7 HSE Silver
RRS TDV8 HSE silver
FFRR Vogue black
Disco3 HSE silver
RRS 2.7 HSE silver
RRS 3.0 HSE BALTI BLUE
______________________________
current vehicles
RRS 3.0 L494 Autobiography
Audi R8 V10 Spyder
AC Cobra
Landrover Defender 90
Landrover Defender 110
Suzuki Jimney