Increasing offset on a very old-school 29er

I have an old Spot Rocker with a 72 degree headangle.

What will happen to me if I put a large offset fork on it?

I’m talking like 55-65mm or something. Currently running 47mm.

I find it a tricky one to get my head around. Luckily others don’t e.g. https://www.theproscloset.com/blogs/news/why-mountain-bike-use-reduced-offset-forks#:~:text=The%20front%20wheel%20feels%20easier,Increasing%20fork%20offset%20reduces%20trail.

[registering interest as someone with a retro 29er with a 72 degree HT]

Lawn needs mowing, just saying.

Yea, the thing is, with an old 29er like this, I don’t have any need to bring the front end back in like the modern LLS things. I also don’t have any need to speed up the handling.

So what I’m wondering is whether, with a short, twitchy, tucked-in front end like I have on this bike, a large offset could actually improve stability somehow (and get rid of the toe overlap I will have if I put a decent size front tyre on there).

I used to have a Stooge MK4 with a 66 deg HA and 80mm fork offset. That thing was somehow both super responsive and stable at the same time. But there were a lot of cases where I didn’t want a wheelbase that long.

So what I’m wondering is whether, with a short, twitchy, tucked-in front end like I have on this bike, a large offset could actually improve stability somehow (and get rid of the toe overlap I will have if I put a decent size front tyre on there).

My understanding is that larger offset will actually reduce the trail and make it less stable.

@thols2, yes, that’s my understanding now too. At first I thought higher offset was just a way for 29ers to gain some of the responsiveness they loose from larger wheels and/or slacker headangles. Hence the geometry of Andy’s Stooges and to a lesser degree some older Singular’s (55mm offset I think). I didn’t realise it also decreased stability (although def didn’t notice that on the 80mm offset Stooge Mk4…)

I wonder how linear the effect is though, given there are so many interactions going on. So if I already have a steep HA and short front end, whether increasing offset is going to make things worse overall, or whether a longer front end will compensate at all.

My other option, which I should prob do in any case, is a Works 1.0 angleset, which they have somehow managed to fit into an old school straight 1 1/8th headset:

https://www.workscomponents.co.uk/10-degree-ec34-ec34-angle-headset—to-suit-1-18-steerer-tube-1047-p.asp

Longer offsets and slacker HTAs for 29ers were Jeff Jones’s thing early on, a few years later the Fargo V1 and Gryphon used the same HTA and offset combo. Then the Jones Plus went further with a 75mm offset and 67 HTA, the Stooges go a bit further with that idea again.

Interestingly for me as a bike nerd early Jones bikes were very short wheelbase (~650mm FC) and though they have a unique mix of agility and stability there’s no escaping the way the shorter trail (~75mm) front end gets pinballed in the rough. The Jones Plus less so as it’s much longer wheelbase for a similar rider position yet the trail increase is only about 10% – that suggests FC and wheelbase do add stability alongside the change in grip/rider position overall vs the front axle. But the Jones Plus is a lot longer, a big difference compared to the older 29er.

imo the added FC that you get from increasing offset 7-17mm here won’t counteract the reduction in trail. The FC difference is ‘a tweak’ but the trail difference is ‘a change’, if that makes sense. You’ll always have a light steering lower trail MTB anyway* so it may work ok, but if the bike feels twitchy now the new fork (I expect) will make that aspect somewhere between worse and unbearable.

Edit, with the same tyre it’s only about 8% less trail than the Jones 29er so all’s not quite as it looks, but the weight distribution is polar opposite.

…having said that there are people who like road/rando bikes with very low trail figures that I just can’t get on with, so it’s subjective. Maybe like them you add a bar bag rather than a frame bag and use that to change how it rides, like my Brompton feels much better with a full bag on the front.

You’ll always have a very light steering low trail MTB anyway so it may work ok, but if the bike feels twitchy now the new fork (I expect) will make that aspect somewhere between worse and unbearable.

Thanks @jameso, that looks like the answer I didn’t want, but did need :-)

So, I guess I either get an angleset and hope 71 degrees will do me, or I just wait for a large Pipedream Alice to come up secondhand (i.e., the bike I sold 2 years ago…)

Ha, I edited my post to say ‘a light steering lower trail MTB’ after checking the numbers rather than being influenced by the photo..

Problem is, if I wanted a more modern steel frame, but belt compatible and made from 853 like this thing, it would likely cost a fortune

How about getting it modified to take a 50mm OD head tube for a taper steerer fork? The larger OD of the new tube means the builder could re-mitre the TT and DT to put the HT on at maybe 69 degrees.

With the space you have between DT and F wheel you could even pop a new tube in coming off the upper DT area to the lower HT area, to support a longer HT and shorter fork (a bit like a BTR’s head tube brace tube but under the DT). Maybe get a new fork done for it at the same time, custom offset.. : )

That hadn’t crossed my mind, but a quick glance at my old LBS in Leeds suggests it wouldn’t be that expensive.

Problem is I live in Switzerland at the moment… That may mean double the cost, and I’m not sure there are anywhere near as many framebuilders.

I will look into it though.