Frankenthumper Evo

If you’re reading this then the chances are you’ve already read about the unholy birth of the Frankenthumper – which basically involved me sticking a 650b wheel in the rear of my Hammerhead Thumper frame instead of the normal 29er one.

If not you can catch the original post here, but basically it made the bike lower, slacker and a lot more fun.

I was so impressed with it that I kept the smaller wheel in place for the Grizedale round of the PMBA Enduro Series last weekend – where it coped fine with 2,000m of climbing and descending over the course of the day.

Frankenthumper Evo
It’s not quite as slack and low as it was, but it still doesn’t look too bad.

Stroke of luck
In fact I’d probably have been happy to just carry on like that, were it not for a helpful man on the internet suggesting that I could fit a longer stroke shock now that there wasn’t as much rear wheel to hit the frame.

Well, one thing led to another and I was lucky enough to source a reasonably priced 2015 Rock Shox Monarch RT Debonair shock with what I hoped would be the correct tune in 200x57mm sizing.

At first I thought it just wouldn’t fit, until it was pointed out to me that – durr – I was supposed to fit offset bushings to reduce the eye-to-eye length of the 10mm longer shock.

Fortunately I had a spare set in the van, donated by my kind pal Scott a while ago – and lo-and-behold they were the correct size.

It was still a bit of a squeeze but it did fit – and my calculations say that swapping from the 190x50mm shock had increased the rear wheel travel from 130mm to 148mm.

First impressions were a bit odd, as I had got used to the super-slammed BB and now the bike felt a bit steeper and higher again. But after the faff of fitting the bushings and swapping shocks I was determined to give it a proper trial.

Rock Shox Monarch RT
The decals on the new shock aren’t the best match, but the price was right.

Very cheeky
Off to Rivington on a sunny Saturday afternoon and I was pleasantly surprised to find I had the hillside almost to myself – so after pedalling up for 20 minutes I took the bike on a very cheeky two-minute downhill which featured a bit of everything – ruts, roots, a gnarly rock garden, steps, steep bits, bus stops, a drop and some lovely natural berms.

The action of the shock was very different to my usual Cane Creek DB Inline. It was very supple and very active – swallowing the lumps easily and with a pleasant whooshing noise that reminded me vaguely of a turbocharged car’s dump valve.

Then it was on to one of my favourite downhill segments – a minute of off-camber corners, roots, steps, chicanes and a drop – and after this I twigged that the shock was running a bit soft.

Popping a bit more air in it and slowing down the rebound brought a big improvement – pulling the rear of the bike almost in line with the Pike at the front in terms of support and feel.

The same run again was much faster and the extra travel made it easier to carry speed and even pedal through rough sections where I’d normally be hanging on and bouncing about.

View from Winter Hill
Ready to descend a different side of Winter Hill to usual, sans chain.

Up to speed
Riding a selection of other trails on the hill, from open moors to steep, tight woods, I quickly adjusted to the new ride position and felt like I was going as fast as usual – or maybe a touch faster in places.

On Rivi’s famous Ice Cream Run for example, the bike felt much quicker and more composed than previously – floating easily over the rough top section.

I must say I preferred the super-low BB, it was just so aggressive and so much fun – but I’m going to persevere with the longer travel for a bit and try to push it a bit harder once I’m used to it.

A second test ride was aborted halfway down the three-minute San Marino downhill when my chain snapped and I realised I’d left the tool on the side in the garage.

I did actually freewheel down to the bottom before pushing back up and Aaron Gwinning it back over the other side of Winter Hill to the van – but more riding is required to form a proper judgement.

I have a sneaking suspicion – based on how it felt pinning it down the San Marino – that the bike’s chassis might be just a little too flimsy for the kind of riding you can do on a 150/150 bike with a 29er wheel in the front.

So watch this space.

Will I ride off into the sunset on my longer-travel steed? Tune in next time to find out…

4 thoughts on “Frankenthumper Evo

  • August 27, 2017 at 10:43 am


    Nice article !

    I have another Hammerhead Thumper and I´m thinking to replace the 190x51mm rear shock for a 200x57mm like you did.

    Based on your experience, will you recommend me to do this ? I also have 27.5+ wheels.

    Looking forward to hear from you soon.

    Thanks !

    • August 27, 2017 at 2:20 pm

      Hi Andres, thanks for the compliment. I wouldn’t recommend using the longer shock, I didn’t like it and found running 29in front and 27in rear wheels was much better.
      If you’re running 27plus I guess that means you’ve already lowered the BB? So perhaps use an angle-adjust headset and/or offset bushings to make the bike slacker – with a longer fork if the BB is then too low.

  • April 10, 2020 at 7:28 pm

    Hello, how can I check if my frame is 120mm or 130m travel? I bought a used Hammerhead Thumper frame and I don’t know how to check it I found x120 and x130 on the internet. I do not know how. Sorry for my English.


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